Holder of electroconductive contactor, and method for producing the same

ABSTRACT

The holder for an electroconductive contact unit according to the present invention uses a silicon wafer having a laminated structure including a first silicon layer, second silicon layer and silicon oxide film which is disposed between the two silicon layers. A small hole is formed in the first silicon layer for coaxially and slidably guiding a head portion of an electroconductive needle member, and a large hole is formed in the second silicon layer for receiving a flange portion of the needle member and a compression coil spring so that the silicon oxide film serves as a stopper for the flange member. Thus, by finishing the surface of the first silicon layer by lapping, the projecting length of the electroconductive needle member can be defined at a high precision. When the object to be tested consists of a silicon wafer, because the holder is made of the same material as the object to be tested, and they undergo a substantial identical thermal expansion, there is no positional shifting of each electroconductive needle member in simultaneously accessing a plurality of points.

TECHNICAL FIELD

The present invention relates to a holder for an electroconductive unitwhich is suitable for use in testing printed circuit boards,semiconductor devices and semiconductor wafers by resiliently urging anelectroconductive needle member by using a compression coil spring, anda method for making such a holder.

BACKGROUND OF THE INVENTION

The same applicant previously proposed an electroconductive contact unitassembly comprising a holder consisting of a plate member serving as asupport member provided with a plurality of holes, and anelectroconductive needle member and compression coil spring received ineach hole to simultaneously access a plurality of points of printedcircuit boards and multi-pin semiconductor devices for the purpose oftesting them or making required measurements (for instance, Japanesepatent laid-open publication No. 6-201725). According to this priorproposal, as there is no need to prepare a large number of tubularholders for the electroconductive needle members, it is possible tominimize the pitch of the electroconductive needle members and adapt theelectroconductive contact unit assembly to a higher level of densitiesof the points to be tested.

When such a holder for an electroconductive contact unit assembly ismade by drilling holes in a plastic plate member which is electricallyinsulating, each hole is given with a first section having a largediameter and a second section having a small diameter so that theprojecting length of the electroconductive needle member may be definedas required. However, machining work such as drilling is unsuitable foraccurately controlling the distribution of the lengths of the twosections in each hole. Therefore, in the case of an electroconductivecontact unit assembly having an extremely large number of contact unitsfor testing semiconductor wafers, fluctuations in the projecting lengthof each electroconductive needle member is inevitable, and there is somedifficulty in achieving a uniform and stable contact for all of theelectroconductive needle members.

Furthermore, there has been a growing demand for semiconductor devicesthat can operate in a high temperature environment, and largesemiconductor wafers (having a diameter of 200 mm, for instance) areoften required to be tested in a high temperature environment.Therefore, the electroconductive contact unit assembly for measuringmultiple points of such semiconductor wafers are also required to have acomparable level of resistance to heat and thermal expansion. However,materials having a comparable level of resistance to heat and a smallthermal expansion coefficient are relatively difficult to work, and thistends to lower the production efficiency.

BRIEF SUMMARY OF THE INVENTION

To achieve such objects, the present invention provides a holder for anelectroconductive contact unit for axially slidably supporting anelectroconductive needle member into and out of the holder, theelectroconductive needle member including a head portion adapted tocontact an object, and an enlarged diameter portion coaxially providedin the head portion and having a larger diameter than the head portion,a compression coil spring being received in the holder for resilientlyurging the enlarged diameter portion in a direction to allow the headportion to project out of the holder, characterized by that: the holdercomprises a first silicon layer formed with a small hole for coaxiallyand slidably guiding the head portion, a second silicon layer formedwith a large hole for receiving the enlarged diameter portion and thecompression coil spring, a silicon oxide film disposed between the twosilicon layers and formed with a communication hole having a samediameter as the small hole and coaxial therewith, and an insulating filmformed over the inner circumferential surface of the small hole, largehole and communication hole, the projecting length of the head of theneedle member being defined by the abutting of the enlarged diameterportion onto the silicon oxide film.

Thus, by using a silicon wafer having a three-layered structure formedby interposing a silicon oxide film with a thickness in the order of 1μm between first and second silicon layers, a small hole can be formedin the first silicon layer for coaxially and slidably guiding the headportion by plasma etching conducted under condition which would notaffect the silicon oxide film, and a large hole can be similarly formedin the second silicon layer for receiving the enlarged diameter portionand the compression coil spring. Also, a communication hole coaxial withthe small hole and having a same diameter as the small hole can beformed in the silicon oxide film by plasma etching under a conditionwhich would not affect the silicon layers. The silicon oxide film servesas a stopper by abutting the enlarged diameter portion of the needlemember. Therefore, by finishing the surface of the first silicon layerby lapping or the like, the projecting length of the electroconductiveneedle member can be defined at a high precision.

The projecting length of the electroconductive needle member can bedefined at a high precision also by providing a holder for anelectroconductive contact unit for axially slidably supporting anelectroconductive needle member into and out of the holder, theelectroconductive needle member including a head portion adapted tocontact an object, and an enlarged diameter portion coaxially providedin the head portion and having a larger diameter than the head portion,a compression coil spring being received in the holder for resilientlyurging the enlarged diameter portion in a direction to allow the headportion to project out of the holder, characterized by that: the holdercomprises a silicon oxide layer formed with a small hole for coaxiallyand slidably guiding the head portion, a silicon layer formed with alarge hole for receiving the enlarged diameter portion and thecompression coil spring, and an insulating film formed over the innercircumferential surface of the large hole, the projecting length of thehead of the needle member being defined by the abutting of the enlargeddiameter portion onto the silicon oxide layer.

If the insulating film is formed by a silicon oxide film, the insulatingfilm can be easily formed on the inner circumferential surface of theholes of the two silicon layers by forming a silicon oxide film in thepresence of oxygen gas.

If the enlarged diameter portion consists of a radial flange portion,and a stem portion projects from the head portion oppositely from theradial flange portion, the large hole being dimensioned so that the stemportion contacts the compression coil spring as the compression coilspring curves under compressive deformation, an electric signal that isrequired to be exchanged between the head portion of theelectroconductive needle member and the compression coil spring can flowaxially along the stem portion up to the point of contact between thestem portion and the compression coil spring, and this contributes tothe reduction in the electric inductance and resistance because theelectric current is not required to be passed through the compressioncoil spring along a spiral path.

The present invention also provides a method for making a holder for anelectroconductive contact unit for axially slidably guiding anelectroconductive needle member into and out of the holder, theelectroconductive needle member including a head portion adapted tocontact an object, and an enlarged diameter portion coaxially providedin the head portion and having a larger diameter than the head portion,a compression coil spring being received in the holder for resilientlyurging the enlarged diameter portion in a direction to allow the headportion to project out of the holder, characterized by the steps of:preparing a silicon wafer having a laminated structure including a firstsilicon layer, second silicon layer and silicon oxide film which isdisposed between the two silicon layers; forming a small hole in thefirst silicon layer for coaxially and slidably guiding the head portion,and a large hole in the second silicon layer for receiving the enlargeddiameter portion and the compression coil spring; forming acommunication hole coaxial with the small hole and having a samediameter as the small hole in the silicon oxide film; and forming aninsulating film over the inner circumferential surface of the largehole, small hole and communication hole.

Thus, by using a silicon wafer having a laminated structure including afirst silicon layer, second silicon layer and silicon oxide film whichis disposed between the two silicon layers, and forming a communicationhole in the silicon oxide film, the projecting length of theelectroconductive needle member can be defined at a high precision bythe enlarged diameter portion received in the large hole abutting thesilicon oxide film.

By forming the holes in the silicon layers by plasma etching conductedunder a condition which would not substantially affect the silicon oxidefilm, the hole forming work can be conducted at a high precisioncomparable to the level of precision of the mask for the plasma etching.Also, because the depth of the hole is defined by the silicon oxidefilm, the pitch of the holes, the diameter and depth of each hole can becontrolled at a high precision in the order ofμm when a plurality ofsuch electroconductive contact units are arranged in parallel to eachother.

By forming the communication hole by plasma etching conducted under acondition which would not substantially affect the silicon layers, thecommunication hole can be formed in the silicon oxide film both easilyand at a high precision.

By conducting the plasma etching for forming the communication hole fromthe side of the small hole, the communication hole having a samediameter as the small hole can be formed at a high precision.

Other features and advantages of the present invention will be describedin the following with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional vertical view of an electroconductivecontact unit embodying the present invention;

FIG. 2(a) is a fragmentary schematic side view showing the step offorming the silicon oxide film;

FIG. 2(b) is a fragmentary schematic side view showing the step offorming the large and small holes;

FIG. 2(c) is a fragmentary schematic side view showing the completedholder;

FIG. 3 is a schematic sectional vertical view of a completed holder;

FIG. 4 is a view similar to FIG. 1 showing an electroconductive contactunit having two moveable ends; and

FIG. 5 is a view similar to FIG. 1 showing a third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are now described in the followingwith reference to the appended drawings.

FIG. 1 is a schematic sectional vertical view of an electroconductivecontact unit 1 embodying the present invention. Typically, a largenumber of such electroconductive contact units 1 are arranged one nextto another to enable simultaneous measurement of a large number ofpoints of an object to be tested.

In this electroconductive contact unit 1, a circuit board 2 such as aburn-in board in provided in a lower part as seen in the drawing, andthe upper surface of the circuit board 2 is provided with a circuitpattern 2 a which defines the upper surface of the circuit board 2. Aplate member 3 serving as a holder embodying the present invention isplaced integrally upon the upper surface of the circuit board 2 as seenin the drawing. The plate member 3 may be joined to the circuit board 2by fastening means such as threaded bolts not shown in the drawing.

The plate member 3 comprises a first silicon layer 4, silicon oxide film5 and second silicon layer 6 which are laminated one over another. Thefirst silicon layer 4 and silicon oxide film 5 are formed with a smallhole 7 passed across the thickness of the two layers, and the secondsilicon layer 6 is formed with a large hole 8 passed across thethickness of the second silicon layer 6 coaxially with the small hole 7.The large hole 8 directly faces the circuit pattern 2 a. The innercircumferential surface of the small and large holes 7 and 8 is coveredby an insulating film 12.

The small hole 7 coaxially and axially slidably supports a head portion9 a of an electroconductive needle member 9, and the large hole 8coaxially receives a radial flange portion 9 b of the electroconductiveneedle member 9 which is more enlarged than the head portion 9 a. Thelarge hole 8 coaxially receives a compression coil spring 10 which has adiameter slightly smaller than the inner diameter of the large hole 8,and is compressed to a prescribed extent between the radial flangeportion 9 b and the circuit pattern 2 a so that the head portion 9 a ofthe electroconductive contact unit 9 resiliently projects outwards. Theelectroconductive needle member 9 is provided with a boss portion 9 cand a stem portion 9 d having a slightly smaller diameter than the bossportion 9 c which project from the radial flange portion 9 b oppositelyfrom the head portion 9 a, and coaxially extend into the compressioncoil spring 10.

The electroconductive contact unit 1 which is assembled as describedabove can be used for testing semiconductor devices by electric contact.When testing an object 11 to be tested, the pointed end of the headportion 9 a of the electroconductive needle member 9 is brought intocontact with a terminal 11 a of the object 11 to be tested as indicatedby the imaginary lines in FIG. 1, and electric signals are exchangedwith the circuit board 2 (circuit pattern 2 a). The imaginary linesindicate the state of the electroconductive contact unit 1 when ancontact is about to be made, and the electroconductive needle member 9will be pushed into the large hole 8 to some extent against the springforce of the compression coil spring 10 when the measurement actuallytakes place.

In the electroconductive contact unit 1 according to the presentinvention, the compression coil spring 10 is somewhat compressed in itsassembled state (standby state) so as to produce a certain pre-stress asillustrated in FIG. 1. The pre-stress stabilizes the position of thefree end of the head portion 9 a.

In the electroconductive contact unit 1 of the present invention,because the compression coil spring 10 curves as it compresses, a partof the inner circumference of the compression coil spring 10 engages thestem portion 9 d. The part of the compression coil spring 10 extendingbetween the point of engagement with the stem portion 9 d of FIG. 1 andthe coil end contacting the circuit pattern 2 a in the standby state(assembled state) consists of a closely wound segment.

Therefore, when exchanging signals with the terminal 11 a, the electricsignals flow along the electroconductive needle member 9 up to the pointof contact between the stem portion 9 d and the compression coil spring10, and then along the compression coil spring 10. However, because thestem portion 9 d is in contact with the closely wound segment 10 a, theelectric signals flow along the closely wound segment 10 a from the stemportion 9 d to the circuit pattern 2 a. Because the electric current canflow along a linear path in the axial direction, instead of flowingalong a spiral path, the electric inductance and resistance can be bothreduced particularly when dealing with high frequency signals.

As shown in the drawing, when the terminal 11 a has a flat surface, theprojecting end of the head portion 9 a of the electroconductive needlemember 9 should be pointed so that any film that may be present on thesurface of the terminal 11 a may be readily pierced, and a favorableelectric contact may be established. When the terminal consists of asolder ball, the projecting end of the head portion 9 a of theelectroconductive needle member 9 should be flat.

An exemplary method of making the plate member embodying the presentinvention is described in the following with reference to FIGS. 2 and 3.The plate member 3 may consist of SOI (silicon on insulator) formed bylaminating the first silicon layer 4, silicon oxide film 5 and secondsilicon layer 6 as shown in FIG. 2(a). The silicon oxide film has athickness, for instance, in the order of 1 μm. The thickness of thefirst silicon layer 4 is highly precisely controlled by applying alapping finish to the surface (the upper surface in the drawings)thereof.

Referring to FIG. 2(b), a pattern mask M1 having an opening for definingthe small hole 7 is placed on the surface (upper surface in the drawing)of the first silicon layer 4, and another pattern mask M2 having anopening for defining the large hole 8 is placed on the surface (lowersurface in the drawing) of the second silicon layer 6. The small andlarge holes 7 and 8 are then formed by using an ASM (advanced siliconetching) device based on plasma etching from above and below asindicated by arrows a and b in the drawing. The plasma etching processis conducted under such a condition (environment and output) that thesilicon oxide film 5 remains substantially intact. Because the depth ofeach hole is defined by the silicon oxide film 5, even when a largenumber of holes are formed in a plate member consisting of a siliconwafer, and the speed of forming each hole may differ from the centralpart thereof to the peripheral part thereof, all of the holes may begiven with a same depth at a high precision.

Referring to FIG. 2(c), a third mask M3 formed with openings each havingan identical diameter as the small hole 7 is placed over the uppersurface of the first silicon layer 4, and the part of the silicon oxidefilm 5 facing the small hole 7 is removed by applying a plasma etchingprocess from the direction indicated by arrow c in the drawing under acondition (environment and output) different from that of the holeforming process illustrated in FIG. 2(b). Thereby, a communication hole12 having a same diameter as the small hole 7 and communicating thesmall hole 7 and large hole 8 with each other is formed in the siliconoxide film 5.

An insulating film 13 is then formed over the inner surface of thethrough hole defined by the small and large holes 7 and 8 and thecommunication hole 12 as illustrated in FIG. 3. This insulating film 13may be formed by heating the SOI wafer in an oxygen environment, andthereby forming a silicon oxide film.

Thus, the radial flange portion 9 b received in the large hole 8 of theelectroconductive needle member 9 is resiliently pushed against thesilicon oxide film 5 under the resilient spring force of the compressioncoil spring 10 so that the radial flange portion 9 b abuts the side ofthe silicon oxide film 5 facing the large hole 8. The shoulder definedby the part of the silicon oxide film 5 facing the large hole 8 thusserves as a stopper for defining the projecting length of the headportion 9 a of the electroconductive needle member 9.

By forming the silicon oxide film 5 as described above, the depth of thesmall hole 7 can be controlled at a high precision in the order of μm.By lapping the surface (upper face) of the first silicon layer 4, thethickness as measured from the silicon oxide film 5 to the surface(upper face) of the first silicon layer 4 can be controlled at a highprecision. As a result, the projecting length of the head portion 9 a(the projecting length as measured from the upper surface of the firstsilicon layer 4 in FIG. 1) can be controlled at a high precision.

The electroconductive contact unit 1 according to the present inventionis suitable for applications where a large number of terminals arerequired to be accessed at the same time for measurement. Although onlyone electroconductive contact unit is illustrated in FIG. 1, it shouldbe understood that the test assembly may include a plurality of suchelectroconductive contact units which are arranged in parallel to eachother in a plate member 3. When an object having a large area such as asilicon wafer (for instance, having a diameter of 200 mm) is required tobe tested at a plurality of points thereof, the plate member 3 shouldhave a correspondingly large area.

When a plurality of points are accessed at the same time by using suchan assembly having a large area, because the present invention allowsthe projecting length of the electroconductive needle members to beuniform at a high precision, a favorable state of contact can beachieved at all times.

In a test involving a high temperature environment as is the case with awafer-level burn-in (WLBI) test for silicon wafers, if there is anyexcessive thermal expansion of the plate member 3, even when oneelectroconductive contact unit is matched with a corresponding point onthe wafer, another electroconductive contact unit remote from the oneelectroconductive contact unit may be unable to match with thecorresponding point on the wafer. However, according to the presentinvention, because the plate member 3 consists of the same material asthe silicon wafer, there is no difference in thermal expansion betweenthem, and such a positional shift can be avoided.

For instance, in the case of an eight-inch silicon wafer having a largenumber (for instance, 22,400) of points to be accessed, it is necessaryto form a same number of holes in the plate member 3. The plasma etchingused in the present invention is suited for simultaneously forming alarge number of holes, and can be readily adapted for mass production.Also, because the plasma etching process can form holes substantially ata same precision level as that of the pattern mask used for the etchingprocess, and the silicon oxide film 5 can be formed to a thickness inthe order of 1 μm, the pitch of the holes, the diameter and depth ofeach hole can be controlled at a high precision in the order of μm.

Thus, according to the present invention, because the shoulder definedbetween the two sections of the hole having different diameters isformed with a silicon oxide film, and serves as a stopper for definingthe projecting length of the electroconductive needle member, thethickness of the first silicon layer as measured between the interfacewith the silicon oxide film and the surface of the first silicon layercan be accurately controlled by appropriately finishing the surface ofthe SOI wafer (the surface of the first silicon layer 4). This, combinedwith the fact that the silicon oxide film is given with a thickness inthe order of 1 μm, allows the projecting length of the electroconductiveneedle member to be controlled at a high precision. Also, because theholder is made of the same material as the object to be tested when theobject to be tested consists of a silicon wafer, and they undergo asubstantial identical thermal expansion, there is no positional shift ofeach electroconductive needle member when simultaneously accessing aplurality of points.

The foregoing description was related to an electroconductive contactunit having only one moveable end, but the present invention is equallyapplicable to an electroconductive contact unit having two moveableends, and such an example is illustrated in FIG. 4. The partscorresponding to the previous embodiment are denoted with like numeralswithout repeating the description of such parts.

In the embodiment illustrated in FIG. 4, a pair of three-layered holders3 are formed symmetric to each other, and are bonded together by using abonding agent or the like. A compression coil spring 10 is coaxiallyreceived in the large hole 8 thereof. The compression coil spring 10 ofthe illustrated embodiment comprises a pair of coarsely wound segmentsformed on either coil end thereof, and a closely wound segment 10 aformed in an intermediate part thereof.

A pair of electroconductive needle members 9 each similar to theelectroconductive needle member of the previous embodiment are providedon either coil end of the compression coil spring 10 with theirprojecting ends facing away from each other. The stem portion 9 d ofeach electroconductive needle member 9 is in contact with the innercircumference of the closely wound segment 10 a.

In this electroconductive contact unit also, the projecting length ofeach electroconductive needle member 9 is defined by the abuttingengagement of the radial flange portion 9 b with the silicon oxide layer5 under the spring force of the compression coil spring 10. Therefore,the projecting length of each electroconductive needle member of theelectroconductive contact unit having two moveable ends can becontrolled at a high precision in a similar manner as in the previousembodiment.

A third embodiment of the present invention is described in thefollowing with reference to FIG. 5. The parts corresponding to theprevious embodiments are denoted with like numerals without repeatingthe description of such parts.

In the embodiment illustrated in FIG. 5, the first silicon layer 4 andsilicon oxide film 5 in FIG. 1 are replaced by a single silicon oxidelayer 14. Thereby, the insulating film on the inner circumferentialsurface of the small hole 7 can be omitted, and the hole forming processmay be accomplished in the two steps of forming the small hole 7 andforming the large hole 8. This contributes to the simplification of themanufacturing process. This embodiment provides otherwise similaradvantages as the previous embodiments.

What is claimed is:
 1. A holder for an electroconductive contact unitfor axially slidably supporting an electroconductive needle member intoand out of the holder, the electroconductive needle member including ahead portion adapted to contact an object, and an enlarged diameterportion coaxially provided in the head portion and having a largerdiameter than the head portion, a compression coil spring being receivedin the holder for resiliently urging the enlarged diameter portion in adirection to allow the head portion to project out of the holder,characterized by that: the holder comprises a first silicon layer formedwith a small hole for coaxially and slidably guiding the head portion, asecond silicon layer formed with a large hole for receiving the enlargeddiameter portion and the compression coil spring, a silicon oxide filmdisposed between the two silicon layers and formed with a communicationhole having a same diameter as the small hole and coaxial therewith, andan insulating film formed over the inner circumferential surface of thesmall hole and large hole, the projecting length of the head of theneedle member being defamed by the abutting of the enlarged diameterportion onto the silicon oxide film.
 2. A older for an electroconductivecontact unit according to claim 1, wherein the insulating film is formedby a silicon oxide film.
 3. A holder for an electroconductive contactunit according to claim 1, wherein the enlarged diameter portionconsists of a radial flange portion, and a stem portion projects fromthe head portion oppositely from the radial flange portion, the largehole being dimensioned so that the stem portion contacts the compressioncoil spring as the compression coil spring curves under compressivedeformation.
 4. A holder for an electroconductive contact unit foraxially slidably supporting an electroconductive needle member into andout of the holder, the electroconductive needle member including a headportion adapted to contact an object, and an enlarged diameter portioncoaxially provided in the head portion and having a larger diameter thanthe head portion, a compression coil spring being received in the holderfor resiliently urging the enlarged diameter portion in a direction toallow the head portion to project out of the holder, characterized bythat: the holder comprises a silicon oxide layer formed with a smallhole for coaxially and slidably guiding the head portion, a siliconlayer formed with a large hole for receiving the enlarged diameterportion and the compression coil spring, and an insulating film formedover the inner circumferential surface of the large hole, the projectinglength of the head of the needle member being defined by the abutting ofthe enlarged diameter portion onto the silicon oxide layer.
 5. A holderfor an electroconductive contact unit according to claim 4, wherein theinsulating film is formed by a silicon oxide film.
 6. A holder for anelectroconductive contact unit according to claim 4, wherein theenlarged diameter portion consists of a radial flange portion, and astem portion projects from the head portion oppositely from the radialflange portion, the large hole being dimensioned so that the stemportion contacts the compression coil spring as the compression coilspring curves under compressive deformation.
 7. A method for making aholder for an electroconductive contact unit for axially slidablyguiding an electroconductive needle member into and out of the holder,the electroconductive needle member including a head portion adapted tocontact an object, and an enlarged diameter portion coaxially providedin the head portion, and having a larger diameter than the head portion,a compression coil spring being received in the holder for resilientlyurging the enlarged diameter portion in a direction to allow the headportion to project out of the holder, characterized by the steps of:preparing a silicon wafer having a laminated structure including a firstsilicon layer, second silicon layer and silicon oxide film which isdisposed between the two silicon layers; forming a small hole in thefirst silicon layer for coaxially and slidably guiding the head portion,and a large hole in the second silicon layer for receiving the enlargeddiameter portion and the compression coil spring; forming acommunication hole coaxial with the small hole and having a samediameter as the small hole in the silicon oxide film; and forming aninsulating film over the inner circumferential surface of the large holeand small hole.
 8. A method for making a holder for an electroconductivecontact unit according to claim 7, wherein the holes in the siliconlayers are formed by plasma etching conducted under a condition whichwould not substantially affect the silicon oxide film.
 9. A method formaking a holder for an electroconductive contact unit according to claim8, wherein the communication hole is formed by plasma etching conductedunder a condition which would not substantially affect the siliconlayers.
 10. A method for making a holder for an electroconductivecontact unit according to claim 9, wherein the plasma etching forforming the communication hole is conducted from the side of the smallhole.